The invention relates to a vehicle with a multiphase electrical machine, with a first onboard electrical sub-system having a first nominal DC voltage and with a second onboard electrical sub-system having a second nominal DC voltage. The electrical machine comprises a rotor, a first stator system and a second stator system. The first onboard electrical sub-system comprises a first inverter with a first link capacitor. The first stator system is associated with the first inverter. The second onboard electrical sub-system comprises a second inverter with a second link capacitor. The second stator system is associated with the second inverter.
Usually, components used in a vehicle constitute electrical energy consumers. These consumers are supplied by an onboard power supply with a nominal voltage of 14 volts. A secondary 12 V energy store that assumes the function of a power source or the function of an energy sink in the onboard electrical system, depending on the operational situation, and a 14 V generator, are designed to provide electrical output of 2-3 kW in the vehicle.
If several consumer loads with a high power requirement are integrated into the onboard electrical system of the vehicle, the onboard electrical system can have two onboard electrical sub-systems. Then, a DC chopper circuit transfers electrical power between the two onboard electrical sub-systems. Besides at least one energy store per onboard electrical sub-system, the electrical machine, which can also be motor-driven in a vehicle with an electrified drive train, also has the function as an electrical power source or sink in the vehicle. Such an onboard electrical system topology is depicted, for example, in DE 102 44 229 A1.
It is an object of the invention to provide an improved vehicle with an electrical machine and two onboard electrical sub-systems, as well as a method for operating the electrical machine.
This and other objects are achieved by a vehicle with a multiphase electrical machine, with a first onboard electrical sub-system having a first nominal DC voltage and with a second onboard electrical sub-system having a second nominal DC voltage, wherein the electrical machine comprises a rotor, a first stator system and a second stator system. The first onboard electrical sub-system comprises a first inverter with a first link capacitor. The first stator system is associated with the first inverter. The second onboard electrical sub-system comprises a second inverter with a second link capacitor. The second stator system is associated with the second inverter. The first stator system is embodied in a star configuration. The second stator system is embodied in a star configuration or a delta configuration. A transfer circuit electrically connects the star point of the first stator system to the higher potential of the second onboard electrical sub-system.
Thus, according to the invention, the first stator system is embodied in a star circuit and the second stator system is embodied in a star circuit or delta circuit, and a transfer circuit connects the star point of the first stator system to the higher potential of the second onboard electrical sub-system. That means that the star point of the first stator system can be coupled with the higher potential of the second onboard electrical sub-system.
According to one preferred embodiment of the invention, the transfer circuit comprises first and second diodes that are connected counter to each other and in series.
Furthermore, the transfer circuit comprises a first switch to which the first diode is connected in parallel or, alternatively, a second switch that is connected to the first diode in parallel.
It is also especially advantageous if the transfer circuit includes the first switch to which the first diode is connected in parallel and the second switch to which the second diode is connected in parallel.
The counter-switched diodes ensure that, when the first switch is open and/or when the second switch is open, the direct electrical coupling between the star point of the first stator system and the higher potential of the second onboard electrical sub-system is ineffective. When the first switch and/or the second switch is closed, there is a direct electrical connection between the star point of the first stator system and the higher potential of the second onboard electrical sub-system in the form of a very low-impedance connection through a series connection of two closed switches or a series connection of a switch and a diode.
In another variant of the invention, the first inverter has three high-side switches and three low-side switches, and the second inverter has three high-side switches and three low-side switches. The three high-side switches of the first inverter and the three low-side switches of the first inverter can be controlled by pulse-width modulation. The three high-side switches of the second inverter and the three low-side switches of the second inverter can be controlled by pulse-width modulation. When the first switch is open and when the second switch is open, the electrical machine can be operated by motor or generator or mixed drive by means of phase-width-modulated control of the high-side switches and of the low-side switches of the first inverter and of the second inverter. A low-side diode and a high-side diode are connected in parallel to the low-side switches and high-side switches, respectively.
This means that the electrical machine can be used with respect to both onboard electrical systems as a generator or a motor—independently of whether the electrical machine of the respective other onboard electrical system is being used as a motor or as a generator at the given time of operation. During operation as a generator, electrical power is fed to the respective onboard electrical system via the respective stator system as a result of a torque applied to the rotor from the outside (e.g., by a combustion engine of the vehicle). During operation as a motor, electrical power is taken from the respective onboard electrical system via the respective stator system and converted into the rotational energy of the rotor, which is taken off of the rotor from the outside (e.g., by a belt-driven consumer of the vehicle) as torque.
It is especially advantageous if the first nominal voltage exceeds the second nominal voltage in the direction of the voltage with respect to a reference voltage in the vehicle, for example, of an electrical mass of the vehicle common to both onboard electrical sub-systems. The electrical machine can be operated as a DC step-down converter between the first onboard electrical sub-system and the second onboard electrical sub-system when the rotor is at a standstill.
The electrical machine can be operated as a DC step-down converter by opening the low-side switches of the second inverter, opening the high-side switches of the second inverter, opening the low-side switches of the first inverter, and controlling the high-side switches of the first inverter by pulse-width modulation.
To reduce conduction losses, the low-side switches of the first inverter can also be controlled by pulse-width modulation complementarily to the high-side switches of the first inverter. In order to prevent a bridge short circuit between the high- and low-side switches, dead time is provided in which both the high-side and low-side switches are open.
In addition, the excitation winding of the rotor can be electrically short-circuited.
If the high-side switches of the first inverter are closed, the differential voltage between the first onboard electrical sub-system and the second onboard electrical sub-system is pending via the effective inductor that is formed by the 3 inductors of the first stator system connected in parallel. During this make-time, the current increases linearly in the inductor, and the mean value thereof can be tapped as direct current by a load. During the switch-off phase, the inductor dissipates the energy content, whereas the link capacitor of the second onboard electrical sub-system is charged. To form a free path for the current, the low-side switches of the first inverter can either be closed or remain open. In the latter case, the low-side diodes of the first inverter are conductive.
In addition, it is especially advantageous if the first nominal voltage exceeds the second nominal voltage in the direction of a higher nominal voltage and the electrical machine can be operated as a DC step-up converter from the second onboard electrical sub-system to the first onboard electrical sub-system when the rotor is at a standstill.
The electrical machine can be operated as a DC step-up converter by opening the low-side switches of the second inverter, opening the high-side switches of the second inverter, opening the high-side switches of the first inverter, and controlling the low-side switches of the first inverter by pulse-width modulation.
To reduce conduction losses, the high-side switches of the first inverter can also be controlled by pulse-width modulation complementarily to the low-side switches of the first inverter. In order to prevent a bridge short circuit between the high- and low-side switches, dead time is provided in which both the high-side and low-side switches are open.
In addition, the excitation winding of the rotor can be electrically short-circuited.
If the low-side switches of the first inverter are closed, the voltage of the second onboard electrical sub-system is pending via the effective inductor that is formed by the 3 inductors of the first stator system connected in parallel. During this make-time, the current increases linearly, and the inductor gains in energy content. At the same time, the high-side diodes of the first inverter close, so that the voltage at the link capacitor of the first onboard electrical sub-system cannot be aligned with the voltage of the second onboard electrical sub-system. During the switch-off phase, the inductor dissipates the energy content, and the link capacitor of the first onboard electrical sub-system is charged. The high-side switches of the first inverter can either be switched on or remain switched off. In the latter case, the high-side diodes of the first inverter are conductive.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
In the drawing figures, the same reference symbols refer to the same technical features.